SAN JUAN, Puerto Rico − A sperm whale beached itself on a coral reef and died in contaminated waters in Puerto Rico on Sunday, officials said.

Authorities found the female whale off Punta Guilarte beach in the southeastern town of Arroyo, said Dr. Antonio Mignucci, director of the Caribbean Stranding Network, a San Juan-based environmental group.

Mignucci estimated that the 30-foot (9-meter) whale was between the ages of 25 and 30, and weighed more than 20,000 pounds (9,000 kilograms). It was atop a reef some 50 feet (15 meters) from shore.

The beach had been closed for some time because of high coliform levels, said Leila Andreu, spokeswoman for the U.S. Caribbean territory's Natural Resources Department.

Mignucci said he didn't think the contaminated waters caused the whale's death. But an autopsy won't be possible because sharks began eating the whale's flesh, he said.

The whale won't be removed from the reef and will decompose naturally, authorities said. Sperm whales have an average life span of between 50 and 60 years, Mignucci said.

Decimated worldwide by commercial whaling, the species is listed as endangered and is protected by the Marine Mammal Protection Act of 1972.

About 15 marine mammals -- mostly manatees -- are found dead each year on or near Puerto Rico's shores, said Mignucci, whose group is dedicated to conserving whales, dolphins and manatees. One or two sperm whales are found dead each year in Puerto Rico, an island of nearly 4 million residents.